Background: Our recent work demonstrated that laminins α4β1γ1 and α5β1γ1, components of the lymph node (LN) stroma, are differentially regulated. Tolerance is associated with relatively higher laminin α4 expression, while immunity is associated with laminin α5 upregulation. These differences resulted in altered regulation of alloreactive T cell and antigen-presenting cell trafficking through high endothelial venules. Here, we tested the hypothesis that laminins directly impact CD4 T cell polarization.

Methods: CD4 T cells from C57BL/6 mice were activated in a pro-Th17 or pro-Treg environment with or without laminin α4 and/or α5. The laminin α5 receptors were blocked with anti-α6 integrin or anti-α dystroglycan mAbs. After 5 days of culture, Foxp3, CD25, and IL17 expression were determined by flow cytometry. For in vivo experiments, TCR Tg CD4cells from TEa mice that recognize donor I-E^d presented by recipient I-A^b were transferred with or without anti-α dystroglycan mAb into C57BL/6 mice that had received CFA/Ea emulsion, and Th17 polarization was analyzed.

Results: Addition of laminin α5β1γ1 to CD4 cells stimulated in a pro-Treg environment reduced the proportion of Treg cells by 2-fold. This effect was abrogated by anti-α6 integrin blocking mAb. The proportion of Treg cells induced by TGFβ was unaltered by the presence of laminin α4β1γ1. However, addition of laminin α4β1γ1 was able to partially reverse the inhibitory effect of laminin α5β1γ1 on Treg induction. In a pro-Th17 environment, the presence of laminin α5β1γ1 increased Th17 induction by 4-fold. This effect was abrogated by anti-α dystroglycan blocking mAb. Addition of laminin α4β1γ1 reduced the proportion of Th17 cells and partially reversed the pro-Th17 effect of laminin α5β1γ1. In vivo, systemic blockade of α-dystroglycan decreased Th17 induction of alloantigen specific CD4 T cells in the lymph nodes of CFA/Ea treated mice.

Conclusions: These results demonstrate that the laminin trimers α4β1γ1 and α5β1γ1 are co-inhibitory and co-stimulatory ligands, respectively, for CD4 T cells. Laminin α5β1γ1 is recognized by the integrin α6 expressed by T cells and inhibits Treg induction. Moreover, laminin α5β1γ1 is also recognized by α-dystroglycan that favors Th17 induction. These data confirmed the immunogenic role of these laminin-specific receptors and suggested a co-stimulatory role for laminin α5β1γ1 in vivo. These findings demonstrate that laminins are not only passive LN structural molecules, but act as molecular switches for tolerance and immunity by directly influencing T cell functions.

CITATION INFORMATION: Simon T, Bromberg J. The Treg/Th17 Axis: A Dynamic Balance Regulated by Stromal Laminins. Am J Transplant. 2017;17 (suppl 3).

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